1. Field of the Invention:
This invention relates to a ratio control spool valve means for adjusting the transmitting motion of a toroidal type infinitely variable traction roller transmission, namely by adjusting the pivoting angle of a pair of opposing power rollers disposed between and in rotative engagement with opposite input and output toric discs.
2. DESCRIPTION OF THE PRIOR ART:
Heretofore, there is a speed controlling means for an infinitely variable transmission such as disclosed in U.S. Pat. No. 4,434,675.
The aforesaid patent relates to a toroidal type infinitely variable transmission which includes; a pair of opposing input and output discs each disposed on input and output shaft, respectively, and define a toroidal cavity therebetween. A pair of motion transmitting power rollers are disposed between the input and output discs and in engagement therewith. A pair of roll support structures each supports a roller and is movable in a direction along of its own pivot axis. A fluid operated actuating means is associated with the support structure for transmitting precess movement to the support structure. At least one of the power roller support structure comprises a circular cam disc connected to the support structure and capable of movement in an axial direction and rotation with the support structure. A main control valve is associated with the circular cam disc and has a control member and a cam follower which contacts the circular cam disc. The main control valves a connected to a pressurized fluid source and to each of the hydraulic operating members for supplying the pressurized fluid to the hydraulic operating members, or releasing hydraulic fluid therefrom when the cam follower is not in a predetermined position. By virtue of this construction, the device of the U.S. Patent, due to the mechanical feedback mechanism constituted by the combination of circular cam disc connected to the power roller support structure and the main control valve cam follower engaging the cam face of the cam disc, can control the transmission ratio in toroidal type infinitely variable transmission means in a very steady manner and by relying on a very simple construction.
However, in the transmission according to the aforesaid U.S. Patent, transmission ratio control is made in such a manner that all instruction signal for rotating and axially moving the support structure is given to the cam follower which engages the cam disc connected to the power roller support structure, and the valve housing is slidably disposed on a threaded support post. Thus, the instruction signal is given by axially moving the valve housing, namely, the valve housing itself has to be moved along the support post. Accordingly, the oil distribution pipings connected to the valve housing have to be made flexible so as to follow the movement of the valve housing, in addition, a relatively large space is required to allow the movement of the valve housing and flexing of the pipings.
Moreover, because the spool in the main valve engages the cam face of the cam disc through a cam follower integral with the spool, the spool is urged to move in response to the rotation and axial movement of the cam disc during the operation. Stroke of the spool travel must be made large enough to avoid its abnormal motion, and yet the stroke of the valve housing also had to be made large.
If the power roller support structure stops either at the upper end or lower end of its stroke at a condition where infinitely variable transmission is in a maximum accelerating position, if an operator moves the valve housing to its maximum decelerating position by a transmission ratio change action, and tries to start the vehicle or other machine, then the necessary stroke S for the spool to shift the power roller to the decelerating side is expressed by a formula mentioned below; EQU TS=S.sub.1 +S.sub.2 +S.sub.3 ( 1)
where
S.sub.1 is the cam lift within the range of transmission change, PA1 S.sub.2 is the valve stroke for preventing abnormal valve action, and PA1 S.sub.3 is the moving stroke of the roller support structure;
For example, if the cam lift S.sup.1 is 6.5 mm, valve stroke S is 0.5.about.1.0 mm and the stroke of the support structure S.sub.3 needs 2 mm at one side, then the total stroke TS becomes 9.5 mm, which is a very large value as compared with ordinary spool valves.
If the necessary stroke TS becomes very large, since the weight of the spool will also become large as the length of the spool becomes longer, then the biasing force of the spool to the precess cam also has to be increased to secure stable valve action, and this results in lengthening of the valve housing as well as its weight. As the result, power means for driving the valve housing for performing transmission ratio change must be made larger, in addition, response characteristics of the device are also degraded due to the increased weight which also increases its cost.